I have tried to ask this question a few times on other forums and have only received cryptic responses but no concrete information.

Here is my situation:

I am outfitting my 38' cheoy lee for some long distance cruising. Currently she has 30gal of tankage for diesel. I would like to expand this by using the boats 100gal integral fiberglass water tank for diesel as well.

I will then add additional tankage in steel tanks for water.

As far as I am aware this should work fine.
Are there issues that I'm not aware of?

The hull is solid (no core).
The tank is sturdy and baffled.
Again, the tank is integral to the hull.

I know I could build the new tanks for diesel but i would prefer not to drink out of an old fiberglass tank.